U.S. patent number 4,130,343 [Application Number 05/770,796] was granted by the patent office on 1978-12-19 for coupling arrangements between a light-emitting diode and an optical fiber waveguide and between an optical fiber waveguide and a semiconductor optical detector.
This patent grant is currently assigned to Bell Telephone Laboratories, Incorporated. Invention is credited to Stewart E. Miller, Kinichiro Ogawa.
United States Patent |
4,130,343 |
Miller , et al. |
December 19, 1978 |
Coupling arrangements between a light-emitting diode and an optical
fiber waveguide and between an optical fiber waveguide and a
semiconductor optical detector
Abstract
A terminating portion of an optical fiber waveguide having a
polished beveled end is laterally disposed directly on the
light-emitting surface of a light-emitting diode (LED). The light
power coupled into the fiber consists of two components: the light
power directly coupled into the fiber all along the region of
contact between the fiber and the light-emitting surface; and the
light power reflected by the beveled end and directed along the
fiber axis.
Inventors: |
Miller; Stewart E. (Locust,
NJ), Ogawa; Kinichiro (Matawan, NJ) |
Assignee: |
Bell Telephone Laboratories,
Incorporated (Murray Hill, NJ)
|
Family
ID: |
25089699 |
Appl.
No.: |
05/770,796 |
Filed: |
February 22, 1977 |
Current U.S.
Class: |
385/49; 385/88;
385/52 |
Current CPC
Class: |
G02B
6/30 (20130101); G02B 6/4203 (20130101); G02B
6/423 (20130101); G02B 6/4214 (20130101); G02B
6/4239 (20130101) |
Current International
Class: |
G02B
6/42 (20060101); G02B 6/30 (20060101); G02B
005/14 () |
Field of
Search: |
;350/96C,96WG,96R
;250/552,227 ;357/17,18,19 ;331/94.5H ;362/32 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Burrus, C. A., Dawson R. W., "Small-area High-current Density GaAs
Electroluminenscent Diodes . . . " Applied Physics Letters vol. 17,
No. 3, Aug. 1970, pp. 97-99. .
L. B. Richards "Photodector as Function Detector" IBM Technical
Disclosure Bulletin vol. 13, No. 3, Aug. 1970, pp.
591-592..
|
Primary Examiner: Corbin; John K.
Assistant Examiner: Hille; Rolf
Attorney, Agent or Firm: Gurey; Stephen M.
Claims
What is claimed is:
1. In combination, a semiconductor optical source having a
light-emitting surface, an optical fiber waveguide having a central
axis, a terminating portion of said fiber waveguide being affixed
to said surface such that the axis of said terminating portion is
substantially parallel to said surface so that a portion of the
light power radiated from said surface is directly refracted into
said optical fiber waveguide, and means at the end of said
terminating portion for reflecting another portion of the light
power radiated from said surface into said optical fiber
waveguide.
2. The combination in accordance with claim 1 wherein said
semiconductor optical source is a light-emitting diode.
3. The combination in accordance with claim 2 wherein said
terminating portion is affixed to said light-emitting surface with
a material having an index of refraction the same as or greater
than the index of refraction of said optical fiber waveguide.
4. The combination in accordance with claim 3 wherein said material
is epoxy.
5. The combination in accordance with claim 2 wherein the
reflecting means is a polished bevel at the end of said optical
fiber waveguide.
6. The combination in accordance with claim 5 wherein said polished
bevel is coated with a reflective metallic material.
7. A combination in accordance with claim 6 which further includes
means for orienting the rotational position and the lateral
position of the beveled end of said optical fiber waveguide on said
light-emitting surface.
8. The combination in accordance with claim 5 wherein said beveled
optical fiber waveguide end makes an angle of 45 degrees with said
light-emitting surface.
9. The combination in accordance with claim 2 wherein said
light-emitting surface is within a groove etched in said
light-emitting diode, said terminating portion of said fiber
waveguide being disposed within said groove.
10. A combination in accordance with claim 9 which further includes
means for orienting the rotational position and the lateral
position of the beveled end of said optical fiber waveguide on said
light-emitting surface.
11. The combination in accordance with claim 10 wherein the
orienting means is a member disposed across said groove.
12. In combination, a semiconductor optical source having a
light-emitting surface, receptacle means attached to said
semiconductor optical source forming a tubular region between said
means and said source having a central axis substantially parallel
to said light-emitting surface, said receptacle means having two
ends, a first end being adapted to receive a terminating end of an
optical fiber waveguide, and the second end including means for
reflecting light power radiated from said surface towards said
first end.
13. The combination in accordance with claim 12 wherein said
semiconductor optical source is a light-emitting diode.
14. The combination in accordance with claim 13 further including
light refractive material disposed within said tubular region.
15. The combination in accordance with claim 14 wherein said light
refractive material has substantially the same index of refraction
as an optical fiber waveguide.
16. The combination in accordance with claim 15 wherein said means
for reflecting light is a planar reflective surface disposed at an
acute angle to said light-emitting surface.
17. A combination in accordance with claim 15 which further
includes an optical fiber waveguide having a terminating end
thereof disposed within said receptacle means through said first
end.
18. In combination, a semiconductor optical detector having a
detecting surface, an optical fiber waveguide having a central
axis, a terminating portion of said fiber waveguide being affixed
to said surface such that the axis of said terminating portion is
substantially parallel to said surface so that a portion of the
light power transmitted in said optical fiber waveguide is directly
refracted into said detecting surface, and means at the end of said
terminating portion for reflecting another portion of the light
power from said optical fiber waveguide into said detecting
surface.
19. The combination in accordance with claim 18 wherein said
semiconductor optical detector is a photodiode.
20. The combination in accordance with claim 19 wherein said
terminating portion is affixed to said light-emitting surface with
a material having an index of refraction the same as the index of
refraction of said semiconductor optical detector.
21. The combination in accordance with claim 20 wherein said
material is epoxy.
22. The combination in accordance with claim 19 wherein the
reflecting means is a polished bevel at the end of said optical
fiber waveguide.
23. The combination in accordance with claim 22 wherein said
polished bevel is coated with a reflective metallic material.
24. A combination in accordance with claim 23 which further
includes means for orienting the rotational position and the
lateral position of the beveled end of said optical fiber waveguide
on said light-emitting surface.
25. The combination in accordance with claim 22 wherein said
beveled optical fiber waveguide end makes an angle of 45.degree.
with said light-emitting surface.
26. In combination, a semiconductor optical detector having a
light-detecting surface, receptacle means attached to said
semiconductor optical detector forming a tubular region between
said means and said detector having a central axis substantially
parallel to said light-detecting surface, said receptacle means
having two ends, a first end being adapted to receive a terminating
end of an optical fiber waveguide, and the second end including
means for reflecting light power radiated from said first end into
said surface.
27. The combination in accordance with claim 26 wherein said
semiconductor optical source is a photodiode.
28. The combination in accordance with claim 27 further including
light refractive material disposed within said tubular region.
29. The combination in accordance with claim 28 wherein said light
refractive material has substantially the same index of refraction
as an optical fiber waveguide.
30. The combination in accordance with claim 29 wherein said means
for reflecting light is a planar reflective surface disposed at an
acute angle to said light-detecting surface.
31. A combination in accordance with claim 29 which further
includes an optical fiber waveguide having a terminating end
thereof disposed within said receptacle means through said first
end.
Description
BACKGROUND OF THE INVENTION
This invention relates to optical fiber waveguides and, more
particularly, to the coupling of light power from semiconductor
light sources to optical fiber waveguides and to the coupling of
light power from optical fiber waveguides to semiconductor optical
detectors.
Optical fiber waveguides are likely to find increased use as the
medium for the transmission of information signals because of their
large signal carrying capabilities. In optical transmission
systems, analog or digital information signals modulate the light
output of a semiconductor source, such as a laser or a
light-emitting diode (LED) and the modulated light power is coupled
to the optical fiber waveguide.
In the prior art, coupling between a light-emitting diode and an
optical fiber is structurally arranged by disposing the optical
fiber on or near the light-emitting area of the light source, such
that the central axis of the fiber is perpendicular to the emitting
area. This structural arrangement, however, has manufacturing
disadvantages. For example, an electrical-to-optical converter will
include a ceramic substrate upon which is mounted a light-emitting
diode connected to an optical fiber waveguide and an integrated
circuit (IC) for driving the LED. When the LED is mounted so that
its light-emitting area is parallel to the plane of the substrate,
the optical fiber emerges perpendicular to the plane of the
substrate which is a disadvantageous arrangement for manufacturing
purposes. Alternatively, if the optical fiber waveguide is mounted
parallel to the substrate, the LED is mounted perpendicular to the
plane of the ceramic substrate. Neither of these prior art
arrangements readily lends itself to a compact structural package.
In addition, the prior art coupling arrangement lacks strength,
since contact between the fiber and LED occurs only at the end of
the fiber. Similar structural problems exist in the prior art
coupling arrangements between optical fiber waveguides and
semiconductor optical detectors.
An object of the present invention is to couple light power from a
semiconductor light source into an optical fiber waveguide.
An additional object of the present invention is to couple light
power from an optical fiber waveguide into a semi-conductor optical
detector.
SUMMARY OF THE INVENTION
In accordance with the present invention, a terminating portion of
an optical fiber waveguide having a reflective end thereon is
laterally disposed on the light-emitting surface of a semiconductor
optical source so that the central axis of the terminating portion
is substantially parallel to the emitting surface. The light power
coupled into the fiber consists of two components: the light power
directly coupled into the fiber all along the region of contact of
the fiber and the light-emitting surface; and the light power
reflected at the end and directed along the fiber axis. Light power
is also coupled from an optical fiber waveguide into a
semiconductor optical detector by similarly disposing the end of a
fiber having a reflective end thereon directly on the light
detecting surface of the optical detector.
In one embodiment the reflective end is a polished bevel on the
optical fiber waveguide. In another embodiment, the optical fiber
waveguide is inserted into a tubular receptacle having a reflective
end thereon and which is filled with a material having an index of
refraction to match the optical fiber. A bonding material such as
an epoxy having an index of refraction the same as or greater than
the index of refraction of the optical fiber waveguide is used to
affix the optical fiber waveguide to the semiconductor optical
source.
A feature of the present invention is that the coupling efficiency
of the arrangement is equivalent to the coupling efficiency of the
prior art end-on coupling arrangement.
An additional feature is that the structural arrangement of the
present invention is more compact and stronger than the prior art
end-on coupling arrangement.
An additional feature is that the present invention is more easily
adaptable to manufacturing processes.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A shows the structural arrangement between a light-emitting
diode and an optical fiber waveguide in accordance with the present
invention;
FIGS. 1B and 1C are cross-sectional views of FIG. 1A;
FIG. 2A shows a second embodiment of the coupling arrangement of
the present invention;
FIGS. 2B and 2C are cross-sectional views of FIG. 2A;
FIGS. 3A, 3B and 3C show modifications of FIG. 2A which include
structural apparatus for positioning the optical fiber on the
light-emitting surface of an LED for maximum coupling
efficiency;
FIG. 4A is an embodiment of the present invention which does not
require a bevel at the end of the optical fiber waveguide; and
FIG. 4B is a cross-sectional view of FIG. 4A.
DETAILED DESCRIPTION
FIGS. 1A, 1B and 1C show an optical fiber waveguide affixed to a
light-emitting diode 100 (LED) in a lateral coupling arrangement in
accordance with the present invention, where FIGS. 1B and 1C are
cross-sectional views of FIG. 1A. The LED 100 is a standard
sandwich heterostructure comprising several n and p type
semiconductor layers. It includes an n-type gallium arsenide, GaAs,
substrate 101 disposed on a metallic conductor 102. An n-type doped
layer 103 of gallium aluminum arsenide, GaAlAs, is disposed on the
substrate 101. Disposed on layer 103 is the active p-type gallium
arsenide layer 104. A p-type gallium aluminum arsenide, GaAlAs
layer 105 is disposed on layer 104 and a p.sup.+ -type gallium
arsenide layer 106 is disposed on layer 105. Metallic conductors
107-1 and 107-2 are disposed on layer 106 forming a narrow groove
therebetween. Conductors 107-1 and 107-2 are electrically connected
together and, when a voltage is impressed between conductors 107-1
and 107-2, and conductor 102, light is emitted from the planar
surface area 108 between conductors 107-1 and 107-2.
In accordance with the present invention, light coupling between
the light-emitting diode 100 and an optical fiber waveguide 110 is
effected by laterally affixing the terminating portion of the
optical fiber waveguide 110 on the emitting area 108 of the diode
so that the axis of the terminating portion is substantially
parallel to the plane of the emitting area 108. The cladding on the
terminating portion of the optical fiber waveguide 110 is removed
by any number of well-known methods and the end of the optical
fiber waveguide is polished to form a bevel 111. As can be noted in
FIG. 1B, the beveled fiber end 111 makes an angle .theta. with
emitting area 108. The light rays that emerge from emitting area
108 at an acute angle are coupled directly into the optical fiber
waveguide all along the area of contact between the emitting area
108 and the waveguide 110. In addition, the polished beveled fiber
end forms a reflector. Thus, the rays that emerge from emitting
area 108 from the region under the bevel that are not directly
coupled into the fiber, are reflected into the fiber waveguide by
bevel 111. In a preferred embodiment, the bevel 111 is coated with
a reflective material 112, such as aluminum. In addition, the
entire terminating portion of the optical fiber waveguide can be
coated with the same reflective material to optically isolate the
light coupled into the waveguide. If the terminating portion of the
optical fiber is coated with a reflective material, the coating is
removed from the circumferential area that is placed in contact
with the emitting surface 108. In order to permanently affix
optical fiber waveguide 110 to the LED 100, the fiber is bonded to
conductor 107 with a material which has a refractive index the same
as or greater than the refractive index of the fiber core, such as
an epoxy. FIG. 1C shows the epoxy material 113 in contact with the
fiber 110 and the conductor 107.
FIGS. 2A, 2B and 2C show a second embodiment of the present
invention in which light power is laterally coupled from a
Burrus-type light-emitting diode 200 into an optical fiber
waveguide 201. FIGS. 2B and 2C are cross-sectional views of FIG.
2A. Rather than etching a circular "well" through the upper
semiconductor gallium arsenide layer to the light-emitting surface
thereunder, as in the typical Burrus diode, a groove is etched
through an n-type gallium arsenide layer 202 to the light-emitting
n-type gallium aluminum arsenide GaAlAs layer 203 thereunder. A
p-type gallium arsenide layer 204 is disposed under layer 203 and a
p-type gallium aluminum arsenide GaAlAs layer 205 is disposed under
layer 204. A p.sup.+ -type gallium arsenide semiconductor layer 206
is disposed under layer 205. A silicon dioxide insulating layer 209
is affixed under layer 206 except for a region 210 directly under
the etched groove. A metallic conductor 208 is disposed under layer
209 and within region 210 under the groove. Metallic conductors are
affixed on the nonetched surface of layer 202. When a voltage is
impressed between conductors 207-1 and 207-2, and conductor 208,
light is emitted from the exposed light-emitting area 211 directly
above region 210.
The exposed core of the optical fiber waveguide 201 having a
polished beveled end 212 is laterally inserted into the groove such
that the fiber end is directly over light-emitting area 211. As
described in connection with the coupling arrangement in FIG. 1A,
the light emitted from the emitting area 211 is directly coupled
into the fiber core 201 all along the region of contact between the
emitting area and the fiber core. In addition, light rays emitted
from the light-emitting area 211 under the bevel that are not
directly coupled into fiber 201 are reflected by the beveled fiber
end 212 and transmitted along the optical fiber waveguide. As
described in connection with the coupling arrangement in FIG. 1A,
increased coupling efficiency is obtained by disposing a reflective
coating 213, such as aluminum, on the beveled fiber end. The
grooved Burrus diode advantageously provides a slot into which the
exposed optical fiber core can be readily positioned. Thus, in a
manufacturing process, there is minimum difficulty in properly
positioning the optical fiber waveguide over the light-emitting
area. As can be noted in FIG. 2C, the gap between the fiber core
201 and the groove is filled with a bonding material such as an
epoxy having an index of refraction the same or greater than the
index of refraction of the fiber core.
Coupling efficiency between the light-emitting diode and the
optical fiber waveguide is a function of the bevel angle, the
lateral position of the terminating portion of the optical fiber
waveguide over the light-emitting area and the rotational position
of the terminating portion on the light-emitting area. Maximum
direct optical power coupling between the light-emitting surface
and the optical fiber waveguide occurs when the entire emitting
surface is in contact with the terminating portion of the fiber.
Maximum reflective coupling occurs when the beveled fiber end is
directly above the emitting area and rotated so that a line
perpendicular to the axis of the etched groove is parallel to the
plane of the bevel. A theoretical analysis shows maximum reflective
light power coupling when the bevel angle is approximately
45.degree. although experimental results show maximum coupling
obtained when the bevel angle is 42.degree..
The structure in FIGS. 3A, 3B and 3C are modifications of the
structure in FIG. 2A. Each structure has provisions for positioning
the fiber directly over the light-emitting area and for orienting
the fiber within the grooved Burrus diode at the rotational
position giving maximum coupling efficiency. A similar numerical
designation is given to the structural elements which are common to
FIGS. 2A, 3A, 3B and 3C. In FIG. 3A, a metallic slab 301 is
connected between conductors 207-1 and 207-2 so that one edge 302
of the slab 301 is perpendicular to the etched groove and is
positioned over the light-emitting area within the groove. Fiber
201 is laterally positioned within the groove until the fiber end
makes contact with slab 301 and is rotated within the groove until
edge 302 is in contact with the planar bevel surface. In FIG. 3B, a
metallic cylindrical rod 303 is disposed perpendicular across the
etched groove between the two conductors 207-1 and 207-2 and above
the light-emitting surface. Fiber 201 is positioned so that rod 303
is disposed across the planar bevel surface. In FIG. 3C, the two
conductors 207-1 and 207-2 are replaced by a unitary U-shaped
conducting member 304 which serves the same purpose and function as
the metallic slab 301 and the metallic cylindrical rod 302 in FIGS.
3A and 3B, respectively.
FIG. 4A shows an embodiment of the present invention which does not
require a bevel at the end of the optical fiber waveguide. FIG. 4B
is a cross-sectional view of FIG. 4A. In FIG. 4A, a metal tube 401
and conductors 207-1 and 207-2 form a receptacle over the
light-emitting surface within the groove of Burrus diode 200. A
planar reflective member 402 is disposed at one end of tube 401
over the light-emitting surface of the light-emitting diode 200.
Member 402 makes an acute, preferably 45.degree., angle with the
light-emitting surface. The other end of tube 401 forms an orifice
with the groove to permit reception of an exposed optical fiber
waveguide core 403 therein. The interior of the tube 401 is filled
with an epoxy matching material 404 having the same refractive
index as the refractive index of optical fiber core 403. Metal tube
401 with its beveled reflective end 402 forms an optical waveguide
from material 404 which directs light emitted from the
light-emitting surface into the optical fiber waveguide 403.
All of the aforedescribed structural arrangements for laterally
coupling a light-emitting diode and an optical fiber waveguide
having coupling efficiencies equal to that obtained with the prior
art end-on coupling. The lateral coupling arrangement of the
present invention, however, provides a stronger and more compact
structure. Although the structural arrangements have been described
in connection with a coupling light emitted from an LED, the
principles of the present invention can be equally employed to
couple light from a semiconductor laser source to an optical fiber
waveguide.
As is readily apparent to one skilled in the art, the principles of
the present invention can also be applied to a coupling arrangement
between an optical fiber waveguide and a semiconductor optical
detector, as for example, a photodiode. In such an embodiment, a
terminating portion of an optical fiber having a beveled end
thereon is disposed on the planar detecting surface of the optical
detector such that the axis of the fiber is substantially parallel
to the axis of the detecting surface. Light power transmitted in
the optical fiber is coupled into the detector directly along the
region of contact between the fiber and the detecting surface and
by reflection at the beveled end. The embodiment of the present
invention illustrated in FIG. 1A could be used to illustrate this
application of the invention wherein LED 100 is replaced by a
semiconductor optical detector, as for example, a simple silicon
backbiased PN junction. The optical fiber waveguide would be bonded
to the surface of the detector with an epoxy having a refractive
index between the refractive indices of the fiber and the
semiconductor detector. The embodiment of the present invention
illustrated in FIG. 4A could also be modified to couple light from
an optical fiber waveguide into a photodiode. In such a
modification, a tubular receptacle having a planar reflective
member at one end is disposed on the detecting surface of a
photodiode in a manner similar to the arrangement in FIG. 4A. When
the tubular receptacle is filled with material having the same
index of refraction as the optical fiber and the optical fiber
inserted within the receptacle, light is coupled from the optical
fiber to the detecting surface of the photodiode. The structural
modifications illustrated in FIGS. 3A, 3B and 3C could also be
modified to orient the fiber on the detecting surface for maximum
coupling efficiency.
The above-described arrangements are illustrative of the
application and principles of the invention. Other embodiments may
be devised by those skilled in the art without departing from the
spirit and scope of the invention.
* * * * *